Dynamics of wave packets in two-dimensional crystals under external magnetic and electric fields: Vortices formation

Abstract

In the present work we deal with the dynamics of wave packets in a two-dimensional crystal under the action of magnetic and electric fields. The magnetic field is perpendicular to the plane and the electric field is on the plane. In the simulations we considered a symmetric gauge for the vector potential while the initial wave packet was assumed to have a gaussian structure with given velocities. The parameters that control the kind of time evolution of the packets are: the width of the gaussian, its velocity, and, the intensity and direction of the electric field as well as the magnitude of the magnetic field. In order to characterize the kind of propagation we evaluated the mean-square displacement (MSD), the participation function and which is more important we were able to follow the wave at different times, which allowed us to see the time evolution of the centroid of the wave packets. A novel effect was observed, namely, the dynamics is such that the wave function \emph{splits} into two or more components and \emph{reconstructs} successively as time goes, vortices are forming. To our understanding this is the first time such an effect is reported. As for the inclusion of the electric field, we observe a complex behavior of the wave packet as well as note that the vortices propagate in direction perpendicular to the applied electric field. A similar behavior presented by the classical treatment, In our case we give a quantum mechanics explanation for that